When speaking, our mouth can be considered as a monopole source (at least as long as the mouth is small in comparison to the wavelength in air). Such a monopole source produces a changing volume over time. This change in volume or better the rate of change (i.e. the derivation of the volume flow) is responsible for the generation of sound.

In the animation the sound field from a breathing cylinder is presented for different frequencies.

Keywords:  

      Monopole
      Volume source
      Point source

